Design principles for tuning selectivity in CO₂ reduction by Fe and Co polypyridine complexes

The development of polypyridine complexes as efficient and selective catalysts for the CO₂ reduction reaction (CO₂RR) remains a central challenge in molecular catalysis for small-molecule activation. Although considerable efforts have been devoted to identifying active catalysts and optimizing their performance under both electrochemical and light-driven conditions, the fundamental principles governing product selectivity have received comparatively less attention. In this review, we highlight recent advances in the development of iron and cobalt polypyridine complexes, with particular emphasis on the molecular design strategies that were found to promote the selective reduction of CO₂ to CO while suppressing the competing hydrogen evolution reaction (HER). Following a brief overview of the mechanistic aspects of the CO₂RR, we discuss how selectivity is influenced by (i) the identity of the metal centre, (ii) the electronic and steric effects of ligand substituents, and (iii) the incorporation of proton transfer relays. Collectively, this survey provides a framework for the rational design of next-generation molecular CO₂RR catalysts and offers valuable guidelines for their integration into efficient solar fuel production systems.